Many devices made of molded plastics, such as containers with covers, have mating parts which are secured together. Many forms of simple locking devices have been proposed to provide security against tampering by children or other unauthorized people. Ideally, such a locking device should provide security against tampering using ordinary hand tools or probes. One example is a rodent bait station having a removable or hinged cover to allow insertion of poison bait at a feeding position within the interior of the station. Many of these stations are made of molded plastic and include integrally molded locking devices. Such locking devices may each comprise one or more resilient barbs located in the cover and one or more ledges mounted in the base. When the cover is closed, the barbs resiliently snap over the ledges to lock the cover to the base. To release the barbs, a flat key having one or more tines is inserted through an opening in the cover and is used as a lever to pry the barbs away from the ledges. Once the lever is released, the resilient barbs return to a locking position.